The mash likely sits for 75 minutes once I get the sparge water going. The recirculation time doesn't count toward the mash time, does it? Im leaving the mash tun alone for a full 60 mins, then recirculating for 10. I've never heard of a longer mash time with lower mash temps. Interesting!
I've been thinking a bit about the relatively low efficiency I get on my system with fly sparging.
I did a Heady clone this last weekend (recipe from on here), mashing at 148F and 1.5 qt/lb, with conditioned grain milled at 0.32" gap on my mill. I use a 10g cooler with a dome false bottom, recirculating via a RIMS tube controlled to 150F. pH was adjusted for my water using most of the gypsum addition called for in the Heady clone recipe, and measured at 5.4 at room temperature at 15 minutes into the mash. (right, that's the background over...)
Relevant to your post quoted above, I used my refractometer to check the SG of the recirculating wort during the 75 minute mash. That lets you check conversion efficiency separately from lautering/sparging efficiency, by comparing to the 100% extraction SG expected at your mash thickness (taken from
Braukaiser). Conversion efficiency was 85% at 60 minutes, about 95% at 75 minutes.
I then did a mash out over 20 mins and fly sparged for about 30 minutes, eventually hitting 70% brewhouse efficiency, and about 75% mash efficiency. So my lauter efficiency wasn't great, but wasn't terrible either for a big beer. I can definitely do better on the sparge, because my final runnings gravity was about 1.020. I guess I could try a lower qt/lb so that I can use more sparge water into the kettle, or compare to batch sparging.
So I suggest you use a refractometer to measure conversion efficiency - this will identify issues with extraction from the grains due to the crush and wetting/recirculation, or incomplete conversion (although starch in solution also contributes to SG), vs lautering efficiency. Have a look at the Braukaiser link above as well, and see what you think you can improve.